Thin-shaped information displays are being demanded at the present time, resulting in implementations of so-called Flat Panel Displays (FPDs). The FPDs include a Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Organic Light Emitting Display (OLED), Field Emission Display (FED), etc. These FPDs differ from each other in mechanisms or methods, such as a light emitting mechanism and an optical valve method, but it is common among the FPDs that optical modulation is performed electrically at respective pixels arranged two-dimensionally on a panel to control light emitted outward from the pixels, and to display images and pictures, etc. These displays need to be provided with an optical valve and a light emitting element at a position corresponding to each pixel, a sophisticated manufacturing process like, e.g., a photoetching process being adopted.
A new display device has been proposed and examined to reduce such a manufacturing load of the sophisticated process. In the display device, light is preliminarily modulated to be guided through a core of an optical waveguide according to total reflections in the core. The light is extracted from a desired position of the core by means of changing a local refractive index at the position of the core. The display device also allows it to reduce the manufacturing load so that what is necessary is just to provide a light extracting element at a position corresponding to each pixel, and the light modulation, i.e., adjustment of light intensity can be made by a light source only.
Japanese laid-open patent application JP-A 1989-193595 (Kokai) disclosed that an element for changing total reflection conditions is provided with a core, upper and lower clads and electrodes disposed on the clads. The core is a multilayer with respective Si and SiN layers laminated by turns, each layer having a thickness of tens of angstroms. The clad covers the surface and rear surface of the core. The electrodes are provided on the clad so that a set of the electrodes is arranged on the surface of the upper clad in a prescribed pitch and in a direction, and the other set is arranged on the surface of the lower clad in a prescribed pitch and in the other direction intersecting with the direction. Furthermore, a planer core is connected with an external light source through a light-intensity modulating device provided to the light source.
The display thus provided modulates light emitted from the light source using the light-intensity modulating device provided to the light source, and the modulated light is guided through the core to a position of a predetermined pixel according to total reflections. The guided light is extracted outward at the position of the core of which refractive index is changed by applying a voltage to the electrodes arranged at each pixel, as the total reflection condition is broken at the position due to the voltage application.
However, the display device disclosed by the Japanese laid-open patent application has an issue that the core indicates only a small change in its refractive index with respect to the voltage application. Lithium niobate (LiNbO3) is often used for a core material having a variable refractive-index, but indicates at most several % changes in the refractive index with respect to a normal voltage-range.
In the related art described above, the refractive index of the core must be changed in order to extract light guided through the core. However, it is difficult to change the refractive index sufficiently so as to extract light, causing a problem that only a small amount of the guided light can be extracted applying a normal-range voltage.